1. Field of the Invention
This invention relates generally to feed screws, and more particularly to a mixing section for a feed screw.
2. Description of the Related Art
Certain embodiments of feed apparatus are known in the art for melting and conveying polymeric material within a cylinder from an inlet to a discharge opening. For instance, conventional extruder and injection screws typically include a feed section, a transition section and a metering section. The conventional screws are rotatable within a cylindrical barrel such that polymer material is conveyed along the barrel. Resin is conveyed from the feed section to the transition section wherein the polymeric material is typically melted with the aid of an external heat source such that the polymeric particles achieve a melted or molten state. The polymeric material then enters the transition section where the volume per unit of length is reduced until the material reaches the metering section. Final melting of any previously unmelted particles is completed as the polymeric material passes through the metering section.
It is desirable to modify the metering section to encourage sufficient mixing of the polymeric material prior to discharge through the discharge opening such that the discharged material is fully melted, homogeneously mixed and uniform in temperature, viscosity, color and composition.
U.S. Pat. No. 5,816,698 to Durina et al. issued Oct. 6, 1998, discloses a feed screw with a metering section wherein the primary flight includes cross channels for communication of material between adjacent portions of a helical channel defined by the primary flight. The metering section is designed such that the cross channel is defined by a continuous transit cut-through channel extending through the metering section in a reverse helical direction with respect to the helical direction of the primary flight. As molten material is advanced by the helical flight, a reverse flow of molten material occurs through the cross channel, thereby recirculating portions of the molten material. However, the prior art fails to disclose a primary flight including a cross channel wherein mixing section may be rotated such that the primary flight causes movement of material at least primarily in the first direction while a mixing segment may cause at least partial cross flow of material through the cross channel substantially in the same direction.
Accordingly, it is an object of the present invention to address and obviate problems and shortcomings of conventional feed screws. More particularly, it is an object of the present invention to provide a mixing section adapted to prevent thermal degradation.
It is another object of the invention to provide a mixing section that encourages chaotic mixing prior to discharging the material.
The above objects are provided merely as examples, and are not limiting nor do they define the present invention nor necessarily apply to every embodiment thereof.
To achieve the foregoing and other objects in accordance with the present invention, a mixing section for a feed screw is provided. The mixing section includes a body portion defined along a longitudinal axis and a primary flight defining a helical channel. The primary flight is helically wound in a first direction about the longitudinal axis and forms a first acute angle with respect to a first plane including the longitudinal axis. The primary flight defines a cross channel to allow fluid communication between adjacent portions of the helical channel. The cross channel is defined along a second plane such that the second plane forms a second acute angle with respect to the first plane. The first and second acute angles are located in the same quadrant and the second angle is less than the first angle.
To achieve further objects of the present invention, a mixing section for a feed screw. The mixing section includes an elongated body including a length extending along a longitudinal axis and a primary flight extending from at least a portion of the length of the elongated body. The primary flight is helically wound about the longitudinal axis to define a helical channel. The primary flight is helically wound in a first direction about the longitudinal axis along at least a portion of the length of the mixing section. The primary flight defines a cross channel to allow fluid communication between adjacent portions of the helical channel. The mixing section further includes a mixing segment extending from the elongated body. The mixing section is adapted to be rotated about the longitudinal axis such that the primary flight may cause movement of material at least primarily in the first direction while the mixing segment may cause at least partial cross flow of material through the cross channel substantially in the first direction.
To achieve further objects of the present invention, a process for making a mixing segment from an elongated cylindrical or conical screw body is disclosed. After providing a cylindrical or conical body, a primary helical flight is defined by defining a first helical groove in the body to define a lead side of the primary helical flight. A second helical groove is further defined in the body to define a trail side of the primary helical flight. The mixing helical flight may be defined by defining a third helical groove in the body to define a lead side of the mixing helical flight and defining a fourth helical groove in the body to define a trail side of the mixing helical flight, wherein the mixing helical flight is defined with a pitch that is greater than the pitch of the primary helical flight. Additional portions of the elongated cylindrical or conical body are then removed to complete the process.
Still other advantages and objects of the present invention will become apparent to those skilled in the art from the following description wherein there are shown and described alternative exemplary embodiments of this invention. As will be realized, the invention is capable of other different, obvious aspects, objects and embodiments, all without departing from the scope of the invention. Accordingly, the drawings, objects and descriptions should be regarded as illustrative and exemplary in nature only, and not as restrictive.